Washington — A changed, yet familiar, Congress resumes work on the budget this week, after Washington's spring recess. It's changed from the first Congress under President Reagan, when his conservative policies crowded Democrats into an ''opposition'' stance, and Republicans marched lockstep behind the White House banner.
The new congressional code words - ''responsibility'' for the Democrats and ''independence'' for Republicans - echo familiar Washington themes from the past.
More important, the trends in both parties lead toward consensus on Capitol Hill between mainstream Democrats and Republican moderates in the months ahead.
This week President Reagan will apply his persuasive powers to Republican leaders in the Senate, where the Budget Committee of Sen. Pete V. Domenici (R) of New Mexico starts the markup of the budget Wednesday. Eager to protect his defense and other spending priorities, he will call GOP leaders to the White House, and will make known his position on the MX missile this week. Wednesday evening he will speak in Pittsburgh on job retraining initiatives.
But the Senate has drifted in a more independent direction, and is expected to resist leaving the White House budget blueprint intact. House Democrats passed their own budget just before the Easter recess.
''In 1981 it was Reagan's agenda - in 1983 it's Congress's agenda,'' observes Norman Ornstein, an expert on Congress for the American Enterprise Institute.
''The House Democratic budget represents a consensus among House Democrats, some Senate Democrats, and moderate Republicans,'' says Ted Van Dyk, president of the Center for National Policy, a new, Democratic-oriented Washington think tank.
''The consensus budget calls for more defense, but less than Reagan wants; taxes to help out with out-year deficits; more job benefits for those hurt by recession; and stopping tax indexing, or putting a cap on tax cuts. . . .''
Mr. Van Dyk predicts that later in the year, GOP Senate leaders will ''embrace an alternative not far from the Democratic House alternative.''
When the President eventually signs on with the House-Senate budget that will emerge from conference between the two chambers, there could be more of a bipartisan tone around Washington as the 1984 campaign begins than most observers might have expected.
Democrats are avoiding an outright ''opposition'' stance. They hope the public will perceive them as responsible, forcing Reagan to more moderate ground.
''That may not be a bad strategy,'' says Van Dyk. ''And it won't be just a Democratic strategy. It'll be a moderate Republican strategy, too.''
The risk for the Democrats is that they could fall into a ''me-too'' stance in 1984, seeking to modify Reagan's program at the edges while powerless against its main thrust.
Yet the Democrats this year have already begun to gain modest credit for offering alternatives to Reagan policies. Last December the public was evenly divided on the assertion that ''the Democrats have no alternative to Reaganomics ,'' according to surveys taken by Penn & Schoen Associates for The Garth Analysis. More recently, there's been a 10-point shift toward the perception that Democrats are offering alternatives.
Unfortunately for the Democrats, Reagan's policies also are viewed with greater favor. Over the same period, the number who say Reagan's policies will help the economy climbed 7 points (from 48 percent to 55 percent), while those who believe his policies will worsen the economy declined 8 points (from 26 percent to 18 percent) in the same surveys.
But the economy may have to perform a lot better than its current tentative recovery to bring Republicans fully back to the Reagan camp.
''The Senate Republicans now are uncertain, in contrast with their ebullience in 1981,'' says the American Enterprise Institute's Mr. Ornstein.
''The message received from the '82 election was that the Republicans in the most trouble were those the least distant from Reagan. Every member of Congress wants campaign insurance. If the economy is going great guns, and Reagan signs an arms agreement with the Soviets, Republicans will want to be in a position to say, 'Vote for the team.' But if Reagan's position erodes, the Republicans want to run as independent individuals.''
In addition, basic divisions within GOP ranks, repressed earlier while Reagan's legislative juggernaut rolled over Capitol Hill, have fully emerged. Division is evident in disputes between the White House and the Hill on the nomination of Kenneth Adelman as arms negotiator, tax withholding on savings account interest, and Caribbean policy, as well as on budget and defense policy.